Government plans to outlaw the creation of embryos which are part-human, part-animal are "unacceptable" and threaten to undermine Britain's leading position in stem cell science, MPs will say today.

A report by the Commons science committee calls on ministers to scrap the proposed ban and accuses the government of basing its opposition to the research on a "deeply flawed" consultation.

The committee's demands - which follow a letter to the prime minister signed by 223 medical charities and patients' groups supporting the research - leave the government increasingly isolated in its intention to prohibit the experiments.

Many scientists believe the research will pave the way for new treatments of diseases such as Alzheimer's, Parkinson's and cystic fibrosis. They want to create animal-human embryos to understand the molecular minutiae behind such conditions. The researchers would pluck a cell from a patient and insert it into a hollowed cow or rabbit egg and stimulate it with a jolt of electricity. The two cells then fuse to make an embryo which is 99.9% human and 0.1% animal. Embryonic stem cells extracted from the embryo could be grown into nerves and other tissues, giving scientists insight into how the disease develops. Under existing laws, the embryos must be destroyed no later than 14 days old and cannot be implanted.

Using plentiful animal eggs will allow the researchers to overcome a major stumbling block caused by the shortage of fresh human eggs that would otherwise be needed for the work. The proposed ban has already drawn criticism from scientists, including Sir David King, the government's chief science adviser, the Human Genetics Commission and the Medical Research Council and Wellcome Trust.

Plans to outlaw the research were revealed in December by the public health minister, Caroline Flint, in a white paper which has become the basis of a wide-ranging overhaul of fertility laws. It recommends a blanket ban on the creation of embryos which are part-animal, part-human, with a provision for some research in the area to be conducted under licence.

The Department of Health defended the proposal by citing a public consultation in which many respondents said they were opposed to the research.

The committee's report calls for the proposals to be dropped from the fertility draft bill, due to be published on May 8. It concludes: "We have found the government's published proposals for future regulation in this area to be unacceptable and potentially harmful to UK science."

At a briefing in London, the committee chairman, Liberal Democrat MP Phil Willis, criticised the public consultation exercise used to defend the ban. The consultation attracted around 300 responses, with 277 opposed to the research, but many came from groups opposed to any research on embryos, he said.

The MPs called for permissive legislation, allowing research into human-animal embryos to go ahead under licence after scrutiny by the fertility regulator, the Human Fertilisation and Embryology Authority. The technique was pioneered by Hui Sheng, a developmental biologist in Shanghai. Scientists at Newcastle University and King's College London have already applied to the HFEA to create animal-human embryos for stem cell research, but their licences are not expected to be granted until the authority completes its consultation in September.

In a statement, a spokesman for the Department of Health said: "Whilst we have proposed an initial ban in general terms, we recognise that there may be potential benefits from such research and are certainly not closing the door to it."

How are hybrid and chimeric embryos made?

There are three different types. Hybrid embryos are made by fertilising an egg with the sperm of another species, the same technique used to make a mule. For a hybrid to fertilise, the egg and sperm have to come from very closely related species. Chimeric embryos are made by injecting cells or genetic material of one species into the embryo of another. Scientists at Stanford University plan to use this to create a mouse with 10% human brain cells.

The third type of embryo is called a cytoplasmic hybrid, created by inserting a cell, or DNA, from one animal into the hollowed-out egg of another species. Scientists in London and Newcastle hope to create these by fusing human cells with cow and rabbit eggs. All research embryos must be destroyed within 14 days and it is illegal for them to be implanted.